fix WRFDA stand-alone da_rad_diags.exe build with GNU Fortran 11

[jamiebresch]

TYPE: bug fix

KEYWORDS: WRFDA, da_rad_diags.exe, gfortran-11

SOURCE: Jamie Bresch (NCAR)

DESCRIPTION OF CHANGES:
Problem:
On MacOS with GNU Fortran (Homebrew GCC 11.1.0_1) 11.1.0, the stand-alone utility da_rad_diags.exe does not build.
The error messages:

gfortran -c -O2 -ftree-vectorize -funroll-loops -w -ffree-form -ffree-line-length-none -fconvert=big-endian -frecord-marker=4 -fallow-argument-mismatch -fallow-invalid-boz  -fdefault-real-8 -I/usr/local/include da_rad_diags.f
da_rad_diags.f:1804:28:

 1804 |    namelist /record1/ nproc, instid, file_prefix, start_date, end_date, cycle_period
      |                            1
Error: Symbol 'nproc' in namelist 'record1' at (1) must be declared before the namelist is declared.
da_rad_diags.f:1804:36:

 1804 |    namelist /record1/ nproc, instid, file_prefix, start_date, end_date, cycle_period
      |                                    1
Error: Symbol 'instid' in namelist 'record1' at (1) must be declared before the namelist is declared.
da_rad_diags.f:1804:49:

 1804 |    namelist /record1/ nproc, instid, file_prefix, start_date, end_date, cycle_period
      |                                                 1
Error: Symbol 'file_prefix' in namelist 'record1' at (1) must be declared before the namelist is declared.
da_rad_diags.f:1804:61:

 1804 |    namelist /record1/ nproc, instid, file_prefix, start_date, end_date, cycle_period
      |                                                             1
Error: Symbol 'start_date' in namelist 'record1' at (1) must be declared before the namelist is declared.
da_rad_diags.f:1804:71:

 1804 |    namelist /record1/ nproc, instid, file_prefix, start_date, end_date, cycle_period
      |                                                                       1
Error: Symbol 'end_date' in namelist 'record1' at (1) must be declared before the namelist is declared.
da_rad_diags.f:1804:84:

 1804 |    namelist /record1/ nproc, instid, file_prefix, start_date, end_date, cycle_period
      |                                                                                    1
Error: Symbol 'cycle_period' in namelist 'record1' at (1) must be declared before the namelist is declared.
make[1]: [da_rad_diags.o] Error 1 (ignored)

Solution:
Move the namelist statement after variable declarations, then the code builds.

LIST OF MODIFIED FILES:
M var/da/da_monitor/da_rad_diags.f90

TESTS CONDUCTED:

1. da_rad_diags.exe is generated after the fix.

RELEASE NOTE: N/A (it is probably not worth mentioning)